The long-term objectives of this proposal are to increase understanding of taste recognition and taste perception. The proposed experiments will be conducted in the fruit fly, Drosophila melanogaster, an organism with a simple gustatory system and robust gustatory behaviors that is amenable to molecular, genetic and electrophysiological approaches. Taste recognition in Drosophila is mediated by sensory neurons on the proboscis, internal mouthparts, legs, wings, and ovipositor. Preliminary studies have characterized a large family of 56 candidate gustatory receptor genes (GRs) and revealed that each gustatory neuron expresses one or a few receptors. How are these different gustatory neurons represented in the brain? In the somatosensory and visual systems, sensory projections are segregated according to the location of the neuron in the periphery to provide a topographic map of stimulus position in the brain. In the olfactory system, projections are segregated according to the odorant receptor that the neuron expresses, such that the quality of an odor is mapped rather than its peripheral position. The proposed experiments are designed to determine the molecular and positional representations of tastes in the brain. The following aims are proposed: (1) to determine if gustatory projections are segregated according to the receptor they express; (2) to determine if they are segregated according to their location in the periphery; (3) to compare gustatory maps with mechanosensory maps; (4) to identify synaptic connections of gustatory neurons. The proposed experiments will provide insight into the logic of taste representations in the brain, with the ultimate aim of understanding how sensory perception is encoded in neural circuits.